A Few Words About S1Q3T3

The S1Q3T3 pattern certainly deserves more than just a few words. For the sake of brevity, though, here are some critical facts that every provider should know.

The S1Q3T3 pattern describes the presence of an S wave in lead I, a Q wave in lead III, and an inverted T wave in lead III. This pattern was first described by McGinn and White in 1935, and is fairly well known as an indication of acute pulmonary embolism. Unfortunately it is not seen in all patients affected by PE. In fact, a large number of patients with PE will have no electrocardiographic abnormalities at all! However, if the S1Q3T3 pattern is seen, there are a few other findings you can check in order to help you close in on a diagnosis. Here are a few important considerations.

The S1Q3T3 pattern does not indicate acute pulmonary embolism

The fact is, an S1Q3T3 pattern is an indication of acute cor pulmonale. Acute cor pulmonale could be described as increased volume and pressure within the right ventricle due to pulmonary hypertension. What causes acute cor pulmonale? Acute bronchospasm, pneumothorax, ARDS, and, you guessed it… pulmonary embolism. It is important to keep these differentials in mind when a patient presents in respiratory distress with the S1Q3T3 pattern.

If you identify an S1Q3T3 pattern, look immediately at leads V1 & V2

If leads V1 and V2 are inverted in conjunction with an S1Q3T3 pattern, this is a very specific finding in acute pulmonary embolism (or other acute cor pulmonale process). This precordial T wave inversion may extend from V1-V4, but in acute PE, V1 and V2 are typically inverted the deepest. This of course, makes perfect sense. If the RV is struggling to pump blood against increased resistance, it is going to begin to strain. Since V1 & V2 give us be best view of the RV on a standard left sided 12-lead, they should show this strain better than the others. Of course, if you wanted a better view, you could always pop on a V4R.

Don’t forget about tachycardia!

Tachycardia is the most likely EKG finding in a patient with acute PE. This tachycardia is usually of the sinus variety, although some may present with atrial fibrillation or atrial flutter.

Well that about sums it up! Don’t get me wrong, there is A LOT more to be said about this topic, but I felt that these were the big ticket items that I should address right now. I admit that there is a special place in my heart for RV strain patterns (no pun intended(well, not initially at least)) so I am sure I will write more about them in the future. I will also address pulmonary embolism H&P in a future post (or two since it is a bit involved).

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Just saw this entry. Very concise and well-written. I think you put S1Q3T3 in its proper perspective – not highly specific in the grand scheme of things, but under the right clinical conditions very helpful and important. Thanks!